Set in London in 2009, the film opens as two people of a certain age find themselves chatting on a dating website and agree to meet for a casual dinner. This is where Roy (Ian McKellan) and Betty (Helen Mirren) come together and after an initial bit of awkwardness—each one utilized a fake name online—they quickly hit it off. Their relationship is not necessarily romantic, per se—Betty just lost her husband a year earlier and is not ready for something along those lines—but they become companions close enough so that when Roy’s bum knee acts up one night, Betty doesn’t think twice about letting him spend the night at her tastefully appointed home. The only fly in the ointment in this otherwise sweet-sounding story is Betty’s grandson Steven (Russell Torvy), who is instantly suspicious of Roy and worries that his vulnerable grandmother is rushing into things far too quickly.

By this point, we already know that Steven’s suspicions are pretty accurate for Roy is a con man who likes fleecing women like Betty out of their savings. He doesn’t so it so much for the money as the sheer thrill of putting something over on the kind of person who might think themselves too smart to fall for a con job in this day and age, and who would certainly be too embarrassed to report it to the police and risk humiliation. With the aid of his partner (Jim Carter), Roy’s plan is to convince Betty that, as a way of planning for their financial futures, they should put their respective bankrolls (with hers clocking in at nearly three million pounds) into a joint account that each will have access to but which he will, of course, drain immediately before disappearing. Although Roy has done variations of this scam many times before, there are a couple of complications this time around. One involves the unexpected reappearance of one of the victims of his previous job. That person is dealt with easily enough (if a bit messily) but there is an added complication in that it seems as if Roy might actually be developing something resembling feelings for Betty, especially after learning of some health issues she has kept quiet.  Before long, the two decide to go on holiday and surprise surprise this is one of those stories where nothing is quite as it seems, and leading to a shocking revelation that most will see coming, at least in the broad strokes.